1. Field of the Invention
The invention relates to nanoparticulate silicone organocopolymers in the form of their aqueous dispersions or water-redispersible powders, to processes for preparing them, and to their use in coating compositions, more particularly for producing thermal insulation composite systems.
2. Description of the Related Art
Thermal insulation composite systems (TICS) are very important in the insulation of buildings, especially external walls of buildings. TICS typically comprise insulating material, plaster layers, and a coating of a coating composition, such as a paint coat, for example. Common insulating materials are glass wool or boards based on polystyrene. Examples of TICS substrates are brick, lime sandstone or concrete. Plaster layers, based typically on mortar, may be applied to the insulating material. As a further layer, generally the uppermost layer, the TICS comprises a coating of a coating composition. The entire system made up of building surface and TICS is also referred to as an exterior insulation and finishing system (EIFS). TICS reduce the loss of heat from buildings. The insulant properties of TICS derive essentially from the presence within the TICS of at least one component having poor thermal conductivity, such as, for example, components which include air pores.
A widespread occurrence in TICS is damage due to condensation. Condensation may occur in the TICS when the TICS is cooled to such an extent by the ambient air that the temperature reaches or falls below the dew point of the air present, for example, within the air pores of the TICS, and, consequently, water condenses out. The occurrence of condensation causes problems particularly in cold seasons, when the heat introduced into the TICS by insulation, for example, is no longer sufficient to evaporate the condensation formed in the TICS and ultimately to release it from the TICS.
The condensation leads to weathering of the TICS, such as, for example, to the insulant becoming wet through, to algal infestation or to delamination of components of the TICS as a result of freezing condensation, and so the thermal insulation capacity of the TICS is restricted and, ultimately, it is damaged to such an extent that it must be renovated or renewed completely.
It is therefore important to design the TICS in such a way as to prevent accumulation of condensation in the TICS or penetration of water from the environment into the TICS.
In order to prevent penetration of water into exterior facades or TICS, coating compositions have to date been modified frequently with organosilicone compounds as a hydrophobicizing additive. For instance, EP-A 0791566 recommends coating compositions based on alkoxysilanes and optionally alkoxy-functional organopolysiloxanes for hydrophobicizing mineral building materials. DE-A 1076946 teaches the use of organopolysiloxanes based on alkylalkoxysilanes and ethylene glycol as additives for hydrophobicizing porous building materials. Other examples are silicone resin paints or silicone-modified silicate paints or emulsion paints. The application of coating compositions with these kinds of modifications results in coated building materials whose surface and also whose capillaries connected to the surface are hydrophobicized. TICS produced accordingly, therefore, have surface hydrophobicity and capillary hydrophobicity, with the result that condensation arising in the form of water vapor in the TICS, for example, is repelled by the hydrophobicized coating and accumulates in the form of water droplets in the TICS. In comparison to thin films of water, water droplets have a low surface area and so evaporate more slowly.
Furthermore, coatings with capillary hydrophobicity generate a high diffusion resistance for water vapor, and so the liberation of condensation from corresponding hydrophobicized TICS is made more difficult. In contrast, in the case of TICS, it would be advantageous for the diffusion resistance for water vapor to decrease toward the air side of the TICS, in order to facilitate the escape of water vapor from the TICS.
EP-A 1833867 describes, for example, the use of copolymers based on ethylenically unsaturated monomers and ethylenically functionalized nanoparticles as coating compositions for building materials. The coatings obtainable therewith, however, are still not sufficiently wettable with water. Moreover, the copolymers described therein are not highly transparent, high transparency in many fields of application constituting an important requirement of coating compositions.